1. Field of the Invention
The present invention relates generally to check valves and, in particular, to duckbill check valves with support assemblies.
2. Description of Related Art
A check valve is essentially a valve which allows fluid to flow in only one direction through a conduit, while closing and preventing back or reverse flow, when back pressure builds up downstream of the valve to a level greater than the upstream fluid pressure head. Check valves are used in various fluid transportation operations and must include some means of allowing a forward flow of liquid yet preventing any backflow.
Conventional elastomeric duckbill check valves have an inlet cuff (or a flange), an outlet bill and a transitional middle part for connecting the cuff and the bill. The bill includes a slit, which opens when fluid is forced through the valve. Typically, existing duckbill check valves have a bill slit length dimension that is equal to or less than one-half the inlet cuff's circumference.
To improve the performance of duckbill check valves, valves have been recently developed in which the width of the bill is larger than the diameter of the cuff. The area of the outlet part in the open position, thus approaches the area of the inlet part, and the headloss decreases. For example, U.S. Pat. No. 5,931,197 to Raftis et al. discloses an asymmetrical valve of this type and U.S. Pat. No. 6,367,505 to Raftis et al. discloses a check valve with an oversized bill.
Additionally, duckbill check valves have been recently mounted to the end of a pipe with the bill in the vertical position. By having the bill in the vertical position, the pipe will drain completely. Moreover, with bills in the vertical position, the stiffness of the duckbill check valve is increased. However, even with bills being placed in a vertical orientation, large diameter elastomeric duckbill check valves that are 36 inches in diameter or larger have a tendency to “droop” or sag under their own weight. The weight of the output area distorts the sealing area and allows backflow of water or sewage, which the valve is supposed to prevent.
As is broadly discussed in U.S. Pat. No. 6,367,505 to Raftis et al., local reinforcements may be embedded in the elastomeric material of a check valve with an oversized bill to enhance the stiffness of the elastomeric portion of the valve. Furthermore, as illustrated in U.S. Pat. No. 4,607,663 to Raftis et al., staggered embedded pads are used to provide sufficient strength for inversion and sagging resistance in a tide gate valve application. Moreover, EP 1077339A2 to Raftis and Duer teaches use of a support body receivable in the tide gate valve cavity but this is directed to reinforcing the transition part, so as to help prevent the tide gate valve from collapsing in and on itself when subject to backflow.
It is therefore an object of the present invention to provide a check valve assembly that overcomes the design problems associated with prior art duckbill check valves and to address the problem of drooping in large check valves. It is another object of the present invention to provide an improved duckbill check valve, which reduces the amount of unwanted backflow by decreasing the tendency of larger check valves to “droop” or “sag” under their own weight. It is further the object of the present invention to provide a support mechanism that can either be embedded or connected to an inner or outer portion of elastomeric material at only one location in the valve.